Open heart surgery is performed on a “still” heart. The patient's blood is circulated by an extracorporeal system, which includes a blood pump, a cardiotomy reservoir and an oxygenator. In operation, blood is drawn from the patient and pumped through the oxygenator and then returned to the patient. In many instances blood is scavenged from the surgical site and this recovered blood is added to the system through the cardiotomy reservoir. As a consequence, surgical debris and air bubbles may be introduced into the system at this point and it is important that the particulate debris and bubbles not be administered to the patient.
It is the conventional standard of care to place a so-called “arterial filter” in the blood line to intercept and capture particles and gas bubbles before the blood is returned to the patient's body. Filters of this type capture both gas bubbles and particles on a filter mesh. However conventional arterial filters are problematic. Typically the volume of an atrial filter is large to maximize the ability of the device to collect and hold gas bubbles. Captured bubbles are retained on the mesh during the entire surgical procedure. Each bubble that is retained reduces the filter mesh surface area available for particulate collection. It is possible that a large particle load will increase the pressure drop across the filter. This “clogging” effect can increase the pressure on the captured bubbles and force them though the filter. As a consequence of this problem the size of the physical membrane of the arterial filter is very large to provide a margin of safety. However this increases the surface area in contact with blood which is undesirable and increases priming volume which is undesirable. It should also be noted that the mesh size of a typical filter is inadequate to capture small bubbles. Consequently the conventional arterial filter is not efficient at handling bubbles and it is improperly sized for the typical particulate load.
It must also be noted that blood is a very delicate organ and surface contact, turbulence and pressure drops within the system can injure the blood. These properties of blood must be accommodated as well.